U.S. Pat. No. 4,361,559 to Varma discloses antinflammatory 17,17 -bis(substituted thio) androstenes of the formula ##STR1## wherein R.sub.1 and R.sub.2 are the same or different and each is alkyl, cycloalkyl or aryl;
R.sub.3 is hydrogen, hydroxy, alkoxy, aryloxy, alkylthio, arylthio, ##STR2## or halogen; R.sub.4 is hydrogen, methyl, hydroxy, ##STR3## or halogen; R.sub.5 is hydrogen or halogen; and PA0 R.sub.6 is carbonyl or .beta.-hydroxymethylene. A broken line in the 1,2-, 6,7- and 15,16-position of a structural formula indicates the optional presence of ethylenic unsaturation.
Included among the compounds covered in the Varma patent is tipredane which has been found to be a highly effective topical antiinflammatory agent.
Tipredane is practically insoluble in water (less than 0.0002 mg/ml at 25.degree. C.); 1:1 hydroalcoholic mixtures of tipredane are unstable under acidic conditions. Furthermore, tipredane itself is susceptible to oxidation. Where it has been attempted to formulate tipredane with a sodium metabisulfite anti-oxidant and a potassium buffer, it has been found that sulfate was formed by the oxidation of metabisulfite. Furthermore, the presence of excess potassium ion in the formulation could lead to the precipitation of potassium sulfate crystals.
Until now, attempts to prepare a stable lotion formulation containing tipredane which overcomes the above stability problems have not been successful.